1. Field of the Invention
The present invention relates generally to articles manufactured by laser shock peening techniques, and, more particularly, to various article constructions exhibiting enhanced compressive residual stress characteristics induced by laser shock peening, such as selectively configured compressive residual stress distribution profiles having a desired asymmetry appearing within processed workpieces or objects, such as an airfoil.
2. Description of the Related Art
Laser shock processing has found use in applications involving the enhancement of certain structural features such as the leading and trailing edges of turbine engine compressor or other airfoils. Various strategies have focused upon finding adequate laser beam spot patterns to process the airfoil. However, little attention has been given to determining useful techniques that can provide desired shockwave groups and accompanying stress distribution profiles.
In a typical application, when a shockwave from a single laser irradiated spot on the surface of a material propagates into the material from the surface, the peak pressure is highest at the surface and then decreases (i.e., attenuates) with increasing depth into the material. If the peak pressure is high enough, namely, above the dynamic yield strength of the workpiece, the shockwave plastically deforms the material below the surface in an amount generally proportionate to the amount that the peak pressure is above the dynamic yield strength.
The plastic yielding gives rise to plastic strain in the material, which creates the compressive residual stresses desired by the process. As the peak pressure of the shockwave decreases with increasing depth below the surface, the amount of plastic strain also decreases. This factor limits the depth of the compressive residual stress that can be introduced into the workpiece.
Various articles of manufacture are provided that exhibit deep compressive residual stress characteristics induced by laser shock peening, such as an asymmetrical or other selectively configured compressive residual stress distribution profile. The article may include a gas turbine engine component such as an airfoil that exhibits an asymmetrical stress distribution profile through the thickness dimension of a thin section of the airfoil. The asymmetrical stress distribution profile will be selectively tailored to produce compressive residual stress properties within the airfoil that have desired behaviors and objectives, such as retarding crack propagation, inhibiting the growth of incipient flaws, strengthening the material at high fatigue locations, increasing the high cycle fatigue strength at specific location, providing a desired shape on curvatures, and other such uses as typically understood in the art.
According to one article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of adjacent non-overlapping laser shock peened surfaces simultaneously formed with one another. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
The spaced-apart relationship between the simultaneously formed, adjacent non-overlapping laser shock peened surfaces is chosen such that the respective shockwaves induced by laser shock peening will encounter one another as they propagate through the article. The shockwaves will intersect at a location disposed generally between the laser shock peened surfaces.
In one form, the encountering shockwaves will interact in a manner generally exhibiting a constructive interference effect. In this manner, the respective deep compressive residual stress regions that extend from each of the adjacent non-overlapping laser shock peened surfaces will overlap and significantly increase the peak pressure experienced by the material in the vicinity of the shockwave intersection plane. Various laser spot beam patterns may be employed to produce selective arrangements of shockwave interaction locations.
According to another article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of opposing laser shock peened surfaces formed at different times and disposed at different ones of opposing sides of the article. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
In this manner of article production, the opposing time-staggered shockwaves induced by laser shock peening will meet at a location apart from a mid-plane of the article, producing an asymmetrical compressive residual stress profile through a thickness dimension of the article. The relative difference between the arrival times of the laser beams used to laser shock peen the opposing sides of the article is chosen to facilitate control of the profile characteristics by selectively determining the interior location where the opposing shockwaves will encounter one another.
According to another article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of opposing laser shock peened surfaces simultaneously formed with one another at different ones of opposing sides of the article using laser beams having different pulse lengths. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
The use of such differential laser beam pulse lengths results in the development of opposing shockwaves induced by laser shock peening that attenuate at different rates as they propagate through the article. This disparate attenuation in the shockwaves will produce compressive residual stress regions extending from the respective laser shock peened surfaces having a stress distribution profile that exhibits an asymmetry along a thickness dimension of the article.
According to another article of manufacture, the article includes a plurality of laser shock peened surfaces including at least one set of laterally offset laser shock peened surfaces simultaneously formed with one another at different ones of opposing sides of the article. The article also includes a plurality of regions each having deep compressive residual stresses imparted by laser shock peening extending into the article from a respective laser shock peened surface.
This lateral offset has the effect of creating an imbalance in the forces that are developed within the article as the shockwaves induced by laser shock peening propagate through the article. This force imbalance exerts a moment force on the material, tending to rotate it around an axis perpendicular to the displacement vector connecting the laterally-offset, opposing laser shock peened surfaces, and laying in the nominal mid-thickness phone between the opposing laser-peened surface.
Additionally, the oppositely-directed shockwaves will interact in a generally asymmetrical manner relative to a mid-plane of the article, producing a shockwave interaction zone generally centered about the mid-plane but exhibiting wing-type portions that extend toward opposite ones of the article surfaces in an oblique manner relative to the mid-plane. A corresponding asymmetrical stress distribution profile will accompany this particular form of shockwave interaction associated with the simultaneous formation of laterally offset laser shock peened surfaces disposed at opposing sides of the article.
Various forms of selective contouring and geometrical reshaping can be accomplished using these shockwave interaction effects. For example, various spatial features such as bending, deformation, and controlled curvatures can be established, formed, or otherwise introduced into the article.
The invention, in one form thereof, is directed to an article including a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of at least two simultaneously formed, non-overlapping adjacent laser shock peened surfaces.
In a preferred form, the article includes a gas turbine engine component such as an airfoil.
In one form, the article includes at least one row of spaced-apart region overlap locations in the article, wherein region overlap location defines an overlap between at least two respective compressive residual stress regions respectively associated with at least two corresponding simultaneously formed, non-overlapping adjacent laser shock peened surfaces.
In another form, the plurality of laser shock peened surfaces includes at least one row of laser shock peened surfaces arranged in spaced-apart overlapping pairs; and the plurality of regions includes at least one row of spaced-apart region overlap locations in the article, wherein each region overlap location defines an overlap between two respective compressive residual stress regions respectively associated with same row nearest neighbor laser shock peened surfaces of adjacent laser shock peened surface overlapping pairs.
In another form, the plurality of laser shock peened surfaces further comprises at least one row of non-overlapping laser shock peened surfaces configured to define at least one row of spaced-apart region overlap locations, wherein each region overlap location defines an overlap between two respective compressive residual stress regions respectively associated with two laser shock peened surfaces in the same row.
In another form, the plurality of laser shock peened surfaces includes at least one row of overlapping laser shock peened surfaces; and the plurality of regions includes at least one row of spaced-apart region overlap locations in the article. Each row of spaced-apart region overlap locations is generally disposed between respective adjacent ones of the laser shock peened surface rows. Moreover, each region overlap location defines an overlap between two respective compressive residual stress regions respectively associated with laser shock peened surfaces of adjacent rows.
In another form, the article further includes a plurality of rows each having a plurality of spaced-apart region overlap locations, wherein each region overlap location defines an overlap between at least two respective compressive residual stress regions respectively associated with at least two corresponding simultaneously formed, non-overlapping adjacent laser shock peened surfaces. The region overlap locations of each respective row of spaced-apart region overlap locations respectively have a substantially identical directional orientation.
The invention, in another form, is directed to an article including a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of at least two simultaneously formed, non-overlapping adjacent laser shock peened surfaces. The article also includes at least one region overlap location in the article, wherein each region overlap location is defined by an overlap between at least two respective compressive residual stress regions respectively associated with at least two corresponding simultaneously formed, non-overlapping adjacent laser shock peened surfaces.
The invention, in another form thereof, is directed to an article including a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of at least two simultaneously formed, non-overlapping adjacent laser shock peened surfaces. Additionally, the plurality of laser shock peened surfaces have a spatial configuration which is sufficient to enable the article to exhibit at least one shockwave constructive interference effect arising during manufacture of the article.
The invention, in another form thereof, is directed to an article having first and second sides generally opposing one another. The article includes at least one pair of opposing laser shock peened surfaces each formed at a different one of the first and second sides of the article. The respective laser shock peened surfaces of at least one of the at least one pair of opposing laser shock peened surfaces are formed at different times. The article also includes a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface.
The invention, in another form thereof, is directed to an article having first and second sides generally opposing one another. The article includes at least one pair of opposing laser shock peened surfaces each formed at a different one of the first and second sides of the article, and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of regions includes at least one set of compressive residual stress regions having different penetration depths and being associated with a respective pair of opposing laser shock peened surfaces formed at different times. Such processing preferably is in the range of 1 nanosecond to 2000 nanoseconds apart in time.
The invention, in another form thereof, is directed to an article having first and second sides generally opposing one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions in the article. Each region has compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of regions includes at least one set of generally opposing compressive residual stress regions each extending from respective laser shock peened surfaces formed at different times at different ones of the first and second sides of the article. Each set of opposing compressive residual stress regions defines an asymmetrical compressive residual stress distribution profile appearing generally along a respective thickness dimension of the article.
In one form, the respective compressive residual stress regions associated with each respective set of opposing regions meet at least in part at a respective location apart from a mid-plane of the article.
The invention, in another form thereof, is directed to an article having first and second sides disposed generally opposite one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of opposing laser shock peened surfaces simultaneously formed at different ones of the first and second sides of the article using respective laser beams having different pulse lengths.
The invention, in another form thereof, is directed to an article having first and second sides generally disposed opposite one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of opposing laser shock peened surfaces simultaneously formed at different ones of the first and second sides of the article. The plurality of regions includes at least one set of compressive residual stress regions having different penetration depths and being associated with a respective set of opposing simultaneously formed laser shock peened surfaces.
The invention, in another form thereof, is directed to an article having first and second sides generally opposing one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of regions includes at least one set of generally opposing compressive residual stress regions each extending from respective laser shock peened surfaces simultaneously formed at different ones of the first and second sides of the article. Each set of opposing compressive residual stress regions defines an asymmetrical compressive residual stress distribution profile appearing generally along a respective thickness dimension of the article.
In one form, the laser shock peened surfaces are formed with laser beams having different pulse lengths.
The invention, in another form thereof, is directed to an article having a first side and a second side generally opposing one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of laterally offset, simultaneously formed laser shock peened surfaces each disposed at a different one of the first and second sides of the article.
In one form, the lateral offset relationship is sufficient to enable associated shockwaves induced by laser shock peening to encounter one another during manufacture of the article.
The invention, in another form thereof, is directed to an article having a first side and a second side generally opposing one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of laterally offset, simultaneously formed laser shock peened surfaces each disposed at a different one of the first and second sides of the article. The article further includes at least one region overlap location in the article. Each region overlap location is defined by an overlap between the respective compressive residual stress regions respectively associated with a respective set of laterally offset, simultaneously formed laser shock peened surfaces.
The invention, in another form thereof, is directed to an article having a first side and a second side generally opposing one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The plurality of laser shock peened surfaces includes at least one set of laterally offset, simultaneously formed laser shock peened surfaces each disposed at a different one of the first and second sides of the article. Each set of laterally offset, simultaneously formed laser shock peened surfaces has a respective lateral offset relationship which is sufficient to enable the article to exhibit a respective shockwave interaction effect arising during manufacture of the article.
The invention, in another form thereof, is directed to an article having a first side and a second side generally opposing one another. The article includes a plurality of laser shock peened surfaces and a plurality of regions each having compressive residual stresses imparted by laser shock peening, wherein each region extends into the article from a respective laser shock peened surface. The article further includes at least one zone of compressive residual stress that is characterized by an asymmetrical stress distribution profile relative to a respective reference plane. Each compressive residual stress zone encompasses at least a portion of each one of a respective set of compressive residual stress regions.
In one form, the plurality of laser shock peened surfaces includes at least one set of opposing laser shock peened surfaces each formed at a different time at a different one of the first and second sides of the article.
In another form, the plurality of laser shock peened surfaces includes at least one set of opposing laser shock peened surfaces simultaneously formed at different ones of the first and second sides of the article using respective laser beams having different pulse lengths.
In another form, the plurality of laser shock peened surfaces includes at least one set of laterally offset laser shock peened surfaces simultaneously formed at different ones of the first and second sides of the article.
One advantage of the invention is that the laser shock peening process can increase the penetration depth of compressive residual stress formed below a laser shock peened surface beyond that available from a single pulse.
Another advantage of the invention is that the laser shock peening process can be used to tailor the sub-surface residual stress profile developed through the thickness of a thin section.
Another advantage of the invention is that asymmetry can be introduced into the stress distribution profile by simultaneously laser shock peening both sides of the thin section in the manner described herein, thereby allowing modification of the profile.
Another advantage of the invention is the availability of better control of the depth of the residual stress below the laser shock peened surface, and the intensity of the interaction of the shockwaves at mid-thickness of the thin section.